Without limiting the scope of the disclosed example embodiment, the patent application its background is described in connection with the oxidative properties of silica gel and related compounds.
Developed countries are setting new standards for the allowable amount of sulfur in diesel. By 2009 the allowable amount of sulfur will be 15/10 ppm in diesel fuel1. Currently, hydrodesulfurization processes are utilized to remove sulfur from fuels. These processes involve high temperatures from 350° C.-700° C. and high pressures of about 3-5 MPa of H22 depending on the quality of the oil.
U.S. Pat. No. 7,713,408 issued to Breivik and Knudsen (2010) teaches a process for the catalytic hydrotreating of a hydrocarbon feed stock containing silicon compounds comprising the steps of contacting the feed stock in presence of hydrogen with a first hydrotreating catalyst being arranged in at least two reactors being connected in series at an outlet temperature of up to 410° C. to reduce content of the silicon compounds in the feed stock; cooling of the feed stock such treated to a temperature of between 280° C. and 350° C.; and contacting the cooled feed stock with a second hydrotreating catalyst at conditions being effective in reduction of sulfur compound and nitrogen compound concentration.
From an economic and environmental point of view, it would be more suitable if low-temperature and low-pressure systems could be developed to remove sulfur from fuels. Higher temperature and pressure processes decrease the catalyst life and involves higher H2 consumption and thus, higher costs. In addition, high-temperature and high-pressure processes result in the generation of H2S, a highly toxic compound.
Another reason why if is important to find another method to remove sulfur is because sulfur compounds such as methyl ethyl dibenzothiophene, 4-methyl dibenzothiophene, 3 methyl dibenzothiophene and others are poorly reactive under the hydrodesulfurization process3-5. In order to decrease the levels of sulfur in gasoline and meet environmental regulations it is necessary to eliminate these sulfur compounds from crude oils.
There are other promising techniques for the removal of sulfur, such as bio-desulphurization, extraction, selective adsorption, extraction with ionic liquids, phase transfer catalysts, and oxidative desulfurization to remove sulfur compounds6-8. Most of these techniques utilize oxidizing agents such as NO2, H2O2 and ter-butyl-hydroperoxide9-10. One advantage of using these techniques is that sulfur can be removed at relatively low temperatures and atmospheric pressure. However, the catalysts utilized in the aforementioned techniques, are made of ruthenium and other expensive metals. In addition, the constant use of strong oxidizing agents such as hydrogen peroxide can also become expensive.
U.S. Pat. No. 4,329,221 issued to Farcasiu et al. (1982) provides a process for reducing the metal, sulfur, and nitrogen content of petroleum residual oils. The process involves contacting a mixture of hydrocarbon feedstock and hydrogen-donor solvent with a catalyst composition comprising a naturally occurring porous metal ore such as manganese nodules.
In addition to the high temperature and high pressure catalysts currently available, there are other techniques for the removal of sulfur, such as, selective adsorption, extraction with ionic liquids, phase transfer catalysts, and oxidative desulfurization to remove these sulfur compounds6-8. For example, Mo/Al2O3 catalysts have been used in the oxidative desulfurization (OD) process using hydrogen peroxide as the oxidizing reagent, it has also been proposed to use Ti3(PW12O40)4 catalyst, which also requires the use H2O29-10. There has been research in oxidative desulfurization using decalin solution with sulfur compounds of dibenzothiophene (DBT), where Bu hydroperoxide (TBHP) was used as the oxidant and molybdenum oxide catalyst supported on resins was used as catalyst11. Superoxides for instance, potassium superoxide, has been demonstrated as an alternative oxidant for the oxidative desulfurization process12. For model compounds of benzothiophene, dibenzothiophene, and a number of selected diesel oil samples, sulfur removal greater than 90% and as high as 99% has been accomplished using potassium superoxide12.
U.S. Patent Publication No. 20100038287 (Menegassi et al., 2010) relates to a process for removing organic silicon compounds from hydrocarbon streams by contact with an adsorbent and hydrogen. The adsorbent is composed of lamellar double hydroxides and group VI-B or group VIII hydrogenating metal. More specifically, the process of the present Invention involves a stage of activation for formation of the lamellar double hydroxide, and maintaining the phase of lamellar double hydroxide by adding water.
Peroxides have been used to oxidize DBT as have oxidizing solvents such as aldehydes and carboxylic acid35-36. For example, it has been reported the use of a surfactant-type decatungstates for the oxidation of DBT. This reaction requires hydrogen peroxide24. Also, oxidative desulfurization of dibenzothiophene catalyzed by Keggin-type H3PMo12O40 and Na3PMo12O4 using hydrogen peroxide as the oxidizing agent is found in the literature25.